Priming device for fluorescent tubes



United States Patent Walter Zangerle, Zurich, Switzerland, assignor to Hans Leuenberger, Zurich, Switzerland i Application March 25, 1957, Serial No.64 8,'427

Claims priority, application Switzerland March 27, 1956 3 Claims. (Cl. 3171-141) The present invention relates to a priming device for fluorescent tubes.

Some known priming devices of this kind consist essentially of a glow discharge relay or of a bi-metal strip relay, and accordingly have the disadvantage of not responding any more to priming when the ambient temperature is too low.

Other known priming devices designed to overcome this disadvantage comprise switching elements which have to be connected directly to the mains and accordingly require, in addition to the terminals corresponding to those of the glow-discharge relay or bi-metal strip relay type, some additional terminals, which makes it impossible to use.;such improved priming devices as replacements for the said glow-discharge or bi-metal strip relay devices without additional fitting operations.

I The present invention has the main object of providing a priming device for fluorescent tubes which has only two terminals to be connected across the fluorescent tube and accordingly can be fitted instead of the said glowdischarge or bi-metal strip type devices, while being insensitive to low ambient'temperatures. Another object of the invention is to provide a priming device which is protected from arcing when the priming operations are automaticallyrepeated owing to failure of the fluorescent tube to ignite for one reason or another in spite of proper functioning of the priming device.

.Withthese and other objects in view I provide a priming device for fluorescent tubes comprising in combination: two-terminals only, in operation shunted across the fluorescent tube, three circuits connected in parallel to thesaid terminals, the first one containing at least one relay coil and a resistor, the second one containing at least a second relay coil and a resistor having a negative temperature co-efiic-ient, and the third one containing a resistor having a positive temperature co-eificient, a magnet core in operative relation to the said two relay coils, an armature in operative relation to the said magnet core, a'relay switch controlling the said second and third circuitssimultaneously and operatively connected to the said armature. The armature and relay switch are spring biased away from the magnet core in the open position and are arranged so that when the armature is actuated responsive to the first relay coil being energized, the relay switch is closed and thereafter the armature is drawn to the magnet core and retained thereat by the remanent magnetism therein. Closing of the relay switch net core and the relay switch is restored to its open position.

Preferably the priming device according to the present invention comprises in additionia normally closed a 2,935,659 Patented May 3, 1960 P ice switch arranged in the said first circuit, a bi-metal strip in operative relation to the said resistor having a negative temperature co-eflicient and operatively connected to the said normally closed switch, the said bi-metal strip, when heated to a predetermined extent by the said resistor having a negative temperature co-eflicient, opening the said normally closed switch and interrupting thereby the said first circuit.

These and other objects and features of my invention will be clearly understood from the following description of a preferred embodiment thereof given by way of example with reference to the single figure of the accompanying drawing which is a wiring diagram of a fluorescent lamp equipped with a priming device according to the present invention.

The priming device 1 has only two terminals 2, 3 which are connected to the heated electrodes 4, 5, respectively, of the fluorescent tube 6. With 7 the usual series throttle is denoted, and with 8 the switch which is to be closed for switching-on the fluorescent tube. The terminals of the mains to which an alternating voltage is applied are denoted 9 and 10.

The priming device 1 has a relay 11 with two coils 12 and 13. The magnet core 14 of the relay acts on the armature .15 which is mechanically connected to the arm 16 of the movable contact piece 17 and is preferably directly fitted wit. The switch arm 16 is under the action of a spring 25 which tends to keep it in the open position. The switch arm may obviously be constructed itself asa spring. The first relay coil 12 is connected on the one hand to the terminal 2 and on the other hand I over a normally closed switch 18 and a high resistance resistor 19 to the fixed contact piece 20 which co-operates with the movable contact piece 17. The contact piece 20 is connected to the terminal 3.

The second relay coil 13 is connected on the one hand likewise to the terminal 2, and on the other hand to a resistor 21 having a negative temperature coeflicient which is in anelectrically and thermally conductive connection to a U-shaped bi-metal strip 22. The bi-metal strip is in turn connected to the contact arm 16. When the bi-metal strip is heated, the switch 18 is opened.

Between the input terminal 2 and the switch arm 16 another resistor 23 is shunted parallel to the elements 13, 21, and 22. This resistor 23 is a usual metal resistor anclaccordingly has a slight positive temperature coefficient; the value of its resistance accordingly increases somewhat when current passes through it while that of the resistor 21 diminishes when current passes through the latter.

When closing the switch 8 firstly a current flows through the priming device in a manner to be described later in more detail which involves heating of the heated electrodes 4 and '5 of the fluorescent tube 6. After a short while this current is interrupted. Owing to the series throttle 7, an excess voltage is set up between the electrodes 4 and 5 which had become capable of emission owing to their being heated, which has the consequence of the tube being ignited.

As soon as the main voltage is applied to the terminals 2, 3 of the priming device 1 owing to closure of the switch 8, the following happens in particular:

In a first circuit 12, 18, 19 flows a current which entails attraction of the armature .15 by the relay core 14 and accordingly a movement of the switch arm 16 against spring bias, so that the contact pieces 17, 26 contact one another. This has the consequence that currents flow then also in a second circuit 13, 21, 22 and in a third circuit 23. The vector sum of these three currents effects heating of the heated electrodes 4, 5 of the fluorescent tube 6. Since the impedances of the second and third circuits are much lower than that of the first circuit, and

since the elements 7, 4 and 5, particularly the throttle 7,

act as series impedances to the three circuits which are then in parallel, the current intensity in the first circuit drops to a very low value which no longer sufiices for holding the switch arm 16 in the closed position against spring bias. The switch arm 16 remains nevertheless firstly in its closing position because the armature 15 owing to its kinetic energy received when being attracted by'the core has come into contact with the core 14 only after the contact pieces 17 and 20 had contacted one another already, and got stuck thereto owing to remanent magnetism. Thereby thecontact pieces 17 and 20 are firmly pressed against one another while the switch arm 16 is slightly deformed.

When the contact pieces 17 and 20 contact one an other, a relatively weak current flows firstly in the second circuit 13, 21, 22 since the resistor 21 is still cold, while the current intensity in the third circuit is relatively high. Owing to the heating of the resistors 21 and 23 the current intensity increases slowly in the second circuit, While it slowly decreases on the other hand in the third circuit.

The alternating magnetic flux induced by the relay coil 13 in the core 16 is initially very low. Owing to the increase of the intensity of the current flowing through the coil 13 this alternating flux slowly increases however, and eventually reaches a positive or negative amplitude at which the remanent magnetic flux (which may be directed in one sense or the other i.e.. either positively or negatively) is just cancelled out. At this moment the armature 15 is no longer retained by the cor-e14, and the switch arm 16 is returned by spring bias very quickly into the open positions illustrated. Thereby a strong voltage surge is set up on the series throttle 7 which effects igniting of the fluorescent tube. rent continuing to flow in the first circuit 12, 18, 19 is too weak for ellecting a renewed attraction of the armature 15, because the voltage across the terminal 2 and 3 is no longer equal to the main line voltage but it is equal to the considerably lower operational voltage of the tube 6.

The switch 13 operated by the bi-metal strip 18 serves for safety purposes. Assuming that the fluorescent tube 6 has not ignited in spite of proper functioning of the priming device 1, cg. because the heated electrodes 4, 5 were extraordinarily cold or because they were no longer sufficiently capable of emission, i.e. because the tube 6 was burnt out. After the opening move of the switch arm 16 then the full mains voltage would lie again across the terminals 2, 3, and the working cycle described would repeat itself. The contact pieces 17 and 20 would accordingly again and again alternately come into contact with, and be separated from, one another. This would involve heating of the contacts so that eventually on an open ng move of the switch arm 16 destructive arcing would occur between these contacts after they had become capable of emission.

This disadvantage is obviated in that the bi-metal strip 22 is heated by the resistor 21, when the tube does not ignite at once, to such an extent that it opens the switch 18 and thereby interrupts the first circuit. The heating by the current passing through the bi-metal strip itself is comparatively small, so that the oi-metal strip may lie only partly or not at all within the second circuit, if desired. The switch arm 16 is firstly no longer returned to the closing position owing to the interruption of the first circuit by the switch 18; this closing is possible then only when the bimetal strip 222 has cooled down so far that thereby the switch 13 is closed. Until then however the contact pieces 17 and 20 warmed by the switching operations only to a negligible extent have likewise cooled down to such an extent that some new switching operation can by no means do any damage to them. The priming device 1 accordingly does not suffer The curapy damage even when the switch -8 is kept permanently c osed.

Ofcourse a fluorescent tube which constantly fails to ignite will eventually be replaced. When however, the heated electrodes 4, 5 were only initially too cold, they will after a repeated passage of current through them, have eventually warmed up sufficiently to secure priming of the tube.

The priming device described operates completely reliably, not only at normal temperatures but also at very low temperatures at which for example in a glow relay no discharge at all takes place under the effect of the mains voltage. The current intensity in the first circuit 12, 13, 19 and the attraction of the armature 15 by the relay core 14 are practically entirely independent of temperature. The time required by the resistor 21 of negative temperature coefiicient for reaching so low a resistance value that the current flowing through it and the coil 13 effects the compensation of the remanent magnetic flux, is slightly dependent on the ambient temperature; however, apart from the fact that the resistor 21 has in practice very small geometrical dimensions and accordingly also a very low heat capacity, and consequently is but little dependent on the ambient temperature, the small influence of this temperature is even favourable. When the required time interval calculated from the closing of the switch arm 16 until the remanent magnetic flux is compensated for, is increased owing to a=very low ambient temperature the heated electrodes 4 and 5 of the fluorescent tube are likewise subject to the flow of a current for a correspondingly longer time'and are consequently heated better than with a constant value of this time interval.

The rate at which the switch arm .16 performs its opening movement at the moment of compensation of the remanent flux is again independent of temperature and very high as compared with the speed of switching attainable with bi'-metal switches. By the sudden interruption of the currents in the second and third circuit, which correspond almost to the whole of the current flowingthrough the series throttle 7, a very powerful voltage surge is generated which greatly favours priming.

Structurally the various components of the priming device 1 are preferably combined into a unit, which can be fitted as a whole instead of the glowor bi-metal-relays hitherto usual into the mountings normally used for these relays.

This is an important advantage as compared with known priming devices which likewise operate at low ambient temperatures with greater reliability of priming than the usual glowor bi-metal-relays. These known priming devices comprise switching elements which have to be connected to the input circuit of the fluorescent tube; they have more than two terminals in that parts only of these devices, but not the devices as a whole have to be shunted parallel to the fluorescent tube. It is consequently not possible to replace glowor bi-metal-relays by these known priming devices, Without further fitting operations. Moreover these devices do not show any safety means, which would protect them from destruction in case of failure of the tube to ignite. t

- It may be remarked that across'the terminals 2, 3 of the priming device a condenser may be connected in order to effect a suppression of wireless interference by the fluorescent tube 6, this condenser affecting in no way the operation of the device.

While I have described herein and illustrated ,in, the accompanying drawing what may be considered a typical and particularly useful embodiment of my said invention 1 wish it to be understood that I do not limit myself to the specific details or dimensions described and illustrated,

for obvious modifications will occur to a person skilled in the art.

What I claim as my invention and desire to secure by Letters Patent, is:

1. A priming device for filamentary electrode fluorescent tubes comprising in combination, a pair of input terminals for connection across the electrodes of a fluorescent tube, a first circuit and a second circuit and a third circuit connected in parallel with one another and across said input terminals, said first circuit including a 'first relay coil and a first resistor, said second circuit including a second relay coil and a negative temperature coefiicient resistor, said third circuit including a positive temperature coefiicient resistor, said first resistor being of a high resistance relative to the resistance of said other resistors, a magnet core in operative relation to said relay coils, an armature in operative relation to said magnet core, a relay switch connected to said armature and controlled thereby between open and closed positions respectively for interrupting and completing said second and third circuits simultaneously, and spring means for biasing said armature and said relay switch into the open position, said armature being arranged and operated responsive to the energization of said first relay coil to move said relay switch to said closed position and thereafter to complete contact between said magnet core and said armature so that said armature is maintained in contact with said magnet core by remanent magnetism therein, said second relay coil being energized responsive to the movement of said relay switch to said closed posi tion and subsequent warming up of said negative temperature coefficient resistor and of said positive temperature coefficient resistor, for generating a magnetic flux cancelling out the remanent magnetism in said magnet core whereupon said armature is released from contact with said magnet core by said spring bias means and said relay switch is restored to its open position.

2. A priming device for filamentary electrode fluorescent tubes comprising any combination, a pair of input terminals for connection across the electrodes of a fluorescent tube, a first circuit and a second circuit and a third circuit connected in parallel with one another and across said input terminals, said first circuit including a first relay coil and a normally closed switch and a first resistor, said second circuit including a second relay coil and a negative temperature coeflicient resistor, said third circuit including a positive temperature coefficient resistor, said first resistor being of a high resistance relative to the resistance of said other resistors, a magnet core in operative relation to said relay coils, an armature in operative relation to said magnet core, a relay switch connected to said armature and controlled thereby between open and closed positions respectively for interrupting and completing said second and third circuits simultaneously, spring means for biasing said armature and said relay switch into the open position, said armature being arranged and operated responsive to the energization of said first relay coil to move said relay switch to said closed position and thereafter to complete contact between said magnet core and said armature so that said armature is maintained in contact with said magnet core by remanent magnetism therein, said second relay coil being energized responsive to the movement of said relay switch to said closed position and subsequent warming up of said negative temperature coeflicient resistor and of said positive temperature coefiicient resistor, for generating a magnetic fiux canceling out the remanent magnetism in said magnet core whereupon said armature is released from contact with said magnet core by said spring bias means and said relay switch is restored to its open position, and a bimetallic strip in operative relation with said negative temperature coeiiicient resistor and connected to said normally closed switch in said first circuit so that responsive to the heating of said bimetallic strip to a predetermined temperature by said negative temperature coefficient resistor said normally closed switch is operated to its open position and said first circuit is interrupted.

3. The priming device as set forth in claim 2 wherein said bi-metallic strip is at least partly connected into said second circuit References Cited in the tile of this patent UNITED STATES PATENTS 1,927,512 Baloun Sept. 19, 1933 2,476,330 Sitzer July 19, 1949 2,714,690 Hamilton Aug. 2, 1955 2,784,288 Moran Mar. 5, 1957 FOREIGN PATENTS 880,175 Germany June 18, 1953 

